@Lizzy sounds like a nice project. How old are the boys? If they are young, like under 8 you may want to check out safety standards - kids have been seriously or fataly injured in beds not meeting specific standards. The CPSC site ( cpsa.gov ) may provide some answers or at least someone to contact. Good luck with your project and do post us the final product. Thanks for posting.

@KMS Woodworks You are so right - didn't read that. In light of that the report done on college students injuring themselves falling out of top bunks might be of interest. It would still be important to follow the standards.

You could use 4x4 for legs and1" plywood or you could use pipe and flanges for an industrial look with the pipe going up to the ceiling and make a ladder (or 3) using pipe and wood or find a piece of extension ladder to use and again attach it to the ceiling. You can buy clip-on lights and maybe a hook on basket for a tiny "nightstand" to hold a clock, IPod/IPhone and other personal bedtime items. You can also get a clip on cup holder and an extending tablet or laptop holder. You can use pipe to also build a frame for the plywood to sit on. I'd you use a full sheet of plywood and you will have about 2 feet left over without mattress on it where you can possibly put a small set of shelves or a backrest incline for reading in bed. I actually like the pipe supports because it will be more masculine looking.